So people are optimizing. Why should they optimize for maximum population?
A shrinking population is terrible as there are less and less people to support existing institutions like social services, infrastructure, healthcare, etc.
A very simple example is social security. It is a net wealth transfer from working age people to retirement age people.
If there's not enough working age people then there is not enough to support the retirement age people.
- Smaller population will need less infrastructure
- They don't plan to support the old
- Pension plans were fit for 20th century, esp. post-WW2, but they can't work anymore
Plot twist: They're going to become the old. They don't seem to have that as part of their calculation...
However even if they have many children it doesn't help them if everybody else doesn't.
Demographically you’re in a world of trouble still, but then having children is actually far more important if society and its safety nets are collapsing.
If 1 person (augmented with AI) can be 5x productive then you can easily support aging population.
At the end of the day, population needs goods and services (not money) to improve their standard of living.
Only much worse because the trend is increasing on both sides - old people being kept alive with expensive treatments, dropping population of working people.
In 1990, CO2 emissions equated CO2 absorption by trees. All the goals about CO2 are about coming back to 1990 levels (minus the surplus). So 1990 levels of population is what we should aim for. If a country depopulates, let’s not increase births.
Japan has had these demographics for a while now but it doesn't seem like they are falling apart. Someone will say-- oh but there economy isn't growing! Better a stagnant economy than a famine or a plague.
The problem with population decline is that most countries are built around the naive assumption of perpetual growth, especially when it comes to social security and welfare systems. Of course most of this can easily be fixed by raising taxes but that would fly in the face of the general trend to give tax breaks to higher incomes, abolish wealth taxes and prefer flat tax rates over progressive ones to prevent "wealth flight".
That kind of research is based on the assumption that the social/cultural trends encouraging people to have less kids continue unabated.
Humans often overcompensate. It is conceivable that a country's population may decline to the point that the threat that poses to its future becomes impossible to ignore – the threat may motivate the general population to change their behaviour, and may lead to the government introducing major incentives to encourage more children. That may lead to the population decline being reversed; but, it may then be difficult to "turn off the tap" of the new culture/policies to stop the population booming again.
There are also countercultural minorities (mostly ultra-conservative religious sects) who stubbornly continue to have lots of kids in spite of the social/cultural forces which discourage mainstream society from doing so. That kind of analysis generally ignores those minorities, because they are so small – true, but if they don't change their ways, eventually they will grow to become the majority, and then we'll be back to population boom again.
Will they eventually change their ways? That is possible, not inevitable. Many of them have been successfully resisting pressure to change their ways for decades; if they haven't succumbed to that pressure yet, why assume it is inevitable that they eventually will? If one considers that there are multiple such countercultural minorities, even if some of them do end up changing course, all it takes is for one to stubbornly resist doing so, for it to eventually become the demographic majority.
Every 40 years, the population halves. As each pair of parents retire, their one child enters the workforce, and their labour is used to cover their parents’ pensions — taxes for state pension, and whatever share of the wealth they generate that ends up as corporate profit for private pension.
I don’t know about South Korea, or indeed the statistics of the incidence rate and duration, but from experience I know that late-stage dementia care in the UK costs about twice the average UK earner’s headline salary. I think this may at least show the way it could go wrong, given this is all just an illustration.